Electrode rod for spark alloying, process for preparing the same, and method of depositing a super abrasive containing, coating
This invention relates to an electrode rod for spark alloying, process for preparing the same, and method of depositing a super abrasive containing coating.
The electrospark alloying (ESA) technique is known for the deposition of a wear-resistant coating on the surface of a metallic article. It is based on the material transfer by and in an electronic spark formed between an electrode rod of hard refractory material and work, whereby the former is molten or evaporated at an intense and instantaneous temperature of 3000xc2x0 to 4000xc2x0 C. to transfer over and deposit a coating, on the surface of a work, which may be made of iron-, nickel-, or copper-based alloy, or titanium, tantalum or molybdenum metal. It is also known to transfer carbon from the electrode to form carbide of an ingredient transition metal of the work, in order to produce a hardened surface.
The ESA technique is described in several works. Elektronnaya Obrabotka Materialov, No. 4, issued in 1978, for example, discusses at pages 86 to 87 the properties of coatings formed by this technique, while the No. 5, 1991 issue describes at pages 66 to 68 the preparation of an electrode rod by self-propagating high temperature synthesis.
As ESA electrodes are principally made of high-melting compounds, such as carbide and boride, of a transition metal, it is known that the coated surface can exhibit a wear resistance several times as high as the base material does. However there are a very limited number of materials available for this purpose since the inherent high melting points usually limit the rate of transfer to the work surface, and tend hardly to leave a deposit of regular composition. Further the preparation of electrode rods involves some unsolved problems.
The Inventors by now have found that the synthesis and deposition of a coating of various high melting compounds can be successfully achieved by ESA with an electrode rod of some specific compositions.
It has been considered that as the spark discharge produces a temperature of several thousands of degrees, if in a limited zone, metastable substances such as diamond and cubic boron nitride provided there would convert to the stable phases of graphite and hexagonal boron nitride, respectively. In contrast, our experiments have shown that such backward process can be essentially held against the intense heating, if for a limited time.
Now we have developed these techniques of invention in order to provide a solution based on such findings solved those problems.
This invention provides a solution for those problems, described above, on the basis of a self-propagating high-temperature synthesis (SHS) as applied to the preparation of electrode rods. The invention essentially employs an electrode rod that is made of mixed powder of elemental materials so composed as to enable an SHS process. Thus the invention further provides a method, which consists of just simple basic steps, for the deposition of a coating of high-melting and hard-working material. Also provided is an electrode rod for such purpose.
A first aspect of the invention consists in: an electrode rod for spark alloying, comprising a compact of a first powder of a first component which comprises a metal selected from a group of Fe, Co, Ni, metals of 4a, 5a and 6a of the periodic table and Si, and a second powder of a second component which is capable of self-propagating high temperature synthesis to form with said first component carbide, nitride, boride, silicide or intermetallic compound comprises, said first and second powders being mixed intimately with each other and formed into an axial rod.
A second aspect of the invention consists in: a method for the production of the electrospark alloying rod, comprising: mixing intimately a first powder of first component and a second powder of second component, said first component comprising at least one selected from Fe, Co, Ni, metals of groups 4a, 5a and 6a, Sn, Zn, Pb, Al and Cu, said second component comprising materials capable of SHS process to form a refractory or intermetallic compound, compressing said mixture, followed or not by further firing, and thereby forming an axial body with a bulk density 0.50 to 0.86 time the theoretical values for the corresponding substances.